Oblique flaw detection using ultrasonic transducers

ABSTRACT

Ultrasonic transducers and methods for detecting oblique flaws in cylindrically-shaped objects using pulse-echo testing are provided. By mounting one or more transducers on a rotary tester for testing manufactured objects such as tubes and bars, offsetting each transducer horizontally from its position if it were to emit a beam that is perpendicular to the object&#39;s outer surface, and actuating the transducer so as to emit an angled beam, oblique surface flaws and internal flaws may be reliably detected without reducing inspection speed, significantly adding to transducer cross-talk, or requiring significant additional hardware or processing.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/845,918 filed Mar. 18, 2013, which is a continuation of U.S.application Ser. No. 12/823,600 filed Jun. 25, 2010, now U.S. Pat. No.8,397,575, which is a continuation of U.S. application Ser. No.11/891,132 filed Aug. 8, 2007, now U.S. Pat. No. 7,757,559, and whichclaims the benefit of U.S. Provisional Application No. 60/931,801, filedMay 25, 2007, all of which are incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The present application relates to an invention for inspecting tubes,bars, pipes, and other objects using ultrasonic transducers. Moreparticularly, the invention is concerned with performing pulse-echotesting to detect oblique flaws in such objects using offset and angledultrasonic transducers.

BACKGROUND OF THE INVENTION

Ultrasonic inspection is commonly used to detect flaws, such as surfaceflaws (e.g., cracks), internal flaws (e.g., voids or inclusions offoreign material), and other defects. It is also used to measure wallthickness in tubes and pipes as well as bar diameters. In what is knownas the pulse-echo method for testing, the same transducer serves both asa transmitter and a receiver of ultrasonic beams or waves used to detectsuch flaws and take such measurements.

When testing using the pulse-echo method, a transducer produces apressure wave referred to as an ultrasonic pulse in response to anelectrical pulse. The pressure wave travels through a coupling mediumbetween the transducer and the tested object. Once the ultrasonic pulsereaches an interface between the coupling medium and the tested object,a portion of the pulse enters the object whereas another portion isreflected back to the transducer (i.e., a partial reflection andtransmission occur). The initially reflected pulse is known as afrontwall echo. The portion of the pulse that enters the objectcontinues until the back wall, where another partial reflection andtransmission occur. This partial reflection is known as the backwallecho. If there is an internal flaw in the tested object for instance, aportion of the ultrasonic pulse is also reflected back to the transducerat the flaw. The flaw can be located knowing the elapsed time betweenthe different reflections.

For automatic flaw testing, a gate is placed between the frontwall andbackwall echoes. Any pulse within the gate area may be peak detected,producing an analog output that can be recorded and that represents aflaw in the tested object. In addition, thickness measurements are madepossible knowing the time difference between the backwall and frontwallecho pulses as well as the velocity of the ultrasonic wave as it travelsthrough the medium of the tested object.

The most widely used pulse-echo process for non-destructive testing ofobjects such as tubes and bars is performed by using ultrasonic rotarytesters. Ultrasonic transducers are mounted on a rotary testing unit ofsuch testers, while the tube or bar to be tested is moved freely throughthe tester. Rotating the transducers in the tester around the tube asopposed to rotating the tube as it is moved through the testereliminates the need for heavy machinery and high power in the case oftesting large and long tubes and bars. The space between the object andtransducers is generally filled with water in order to provide couplingfor the ultrasonic beam. The electrical signals from the ultrasonicinspection instrument are connected to the rotating transducers byrotary capacitors. In order to detect various kinds of surface andinternal flaws and to provide thickness measures, several transducersmay be mounted on the tester, each being oriented to perform a specificfunction.

For instance, in a longitudinal wave inspection arrangement, atransducer is typically oriented so that the ultrasonic beam isperpendicular to the surface of the tested object. In such a case, theangle of incidence is 90 degrees. The resulting longitudinal wavestravel along a path that is aligned with the radial axis of the testedobject and are therefore suitable for taking thickness or diametermeasurements and detecting certain inner flaws.

When the angle of incidence is not 90 degrees, refraction occurs and theultrasonic beam splits into two parts in a solid material: alongitudinal wave beam and a shear wave beam. In longitudinal waves,particle motion is parallel to the direction of wave propagation. Inshear waves, however, particle motion is perpendicular to the directionof wave propagation. The refraction angle of the longitudinal wave beamis greater than that of the shear wave beam. Accordingly, when the angleof incidence exceeds a particular value, the longitudinal wave beamceases to exist and only the shear wave beam remains. This angle iscalled the first critical angle. Shear waved can be used to detect bothsurface and internal flaws.

For flaw detection of surface and internal flaws in tubes and bars,shear wave testing is commonly used. FIG. 1 illustrates a setup forperforming one type of such a test on a tube. To improve thedetectability of irregularly shaped flaws, shear waves are generated inboth clockwise and counter-clockwise directions simultaneously using twooffset transducers 110. Each incident beam 120 of transducers 110 ismaintained within the same plane of a cross section that isperpendicular to longitudinal axis 150 of tube 130, while offsetting itfrom radial axis 180. The magnitude of offset is proportional to thediameter of the tube.

Under the setup of FIG. 1, beams 122 and 144 travel generally clockwiseand counter-clockwise, respectively, in the plane of cross section,bouncing between the outer and inner surfaces of tube 130 until a flawis detected and beam 120 is partially reflected back to transducer 110.As shown in FIG. 1, the beam traveling clockwise, beam 122, is reflectedback from an inner diameter crack 160, while the beam travelingcounter-clockwise, beam 144, is reflected back from an outer diametercrack 170.

Such an arrangement, whereby the transducer is offset while its beamremains within the same plane of the tube's cross section, is suitablefor detecting longitudinal flaws, i.e., flaws that are generallyparallel to the tested object's longitudinal axis. However, in order todetect transverse flaws (i.e., flaws that are generally perpendicular tothe tube's longitudinal axis), another arrangement is more appropriate.More specifically, the transducer is preferably angled in a planecontaining the tube's longitudinal axis without offsetting thetransducer from its position when it performs longitudinal wave testing.FIG. 2 illustrates a setup for performing such a test on a tube.

In FIG. 2, transducer 210 is angled in a plane containing longitudinalaxis 150 and radial axis 180 of tube 130 without offsetting transducer210 from its position when it performs longitudinal wave testing.Incident beam 120 of transducer 210 is maintained within the same planeof radial axis 180 and longitudinal axis 150 of tube 130 withoutcreating the offset depicted in FIG. 1. Beam 222 of transducer 210travels generally along the length of tube 130, in the plane containingradial axis 180 and longitudinal axis 150, bouncing between the outerand inner surfaces of tube 130 until a flaw is detected and beam 120 ispartially reflected back to transducer 110. Beam 222 is partiallyreflected back from transverse crack 260 and beam 220 is partiallyreflected back to transducer 210. Transducer 210 can be oriented forforward-, or reverse-looking shear wave testing.

Referring to both FIGS. 1 and 2, tube 130 can be scanned if a set oftransducers is rotated around longitudinal axis 150 while tube 130 isfreely moved along longitudinal axis 150. To allow for thicknessmeasurement and to ensure full flaw detection, several transducers aremounted in the rotary tester. Transducers can be oriented generally forlongitudinal wave testing, while other transducers can be oriented forclockwise and counter-clockwise shear wave testing as shown in FIG. 1and yet other transducers can be oriented for forward-, andreverse-looking shear wave testing as shown in FIG. 2. In this manner,five channels are required so that each transducer can be individuallydriven to achieve full-volume testing that measures thickness anddetects internal flaws as well as surface flaws.

The above discussion outlines how shear waves can be used to detectinternal or surface flaws. Offsetting a transducer without angling it,as shown in FIG. 1, can be used to detect longitudinal flaws, but willvery likely miss transverse flaws. On the other hand, angling atransducer without offsetting it, as shown in FIG. 2, can be used todetect transverse flaws but will very likely miss longitudinal flaws.The orientations of longitudinal and transverse flaws may vary +/−5degrees and still be detected by either offsetting or angling thetransducer. However, such shear wave testing will likely miss naturallyoccurring flaws which are more commonly oriented at some angle such thatthey are neither longitudinal nor transverse given that the largerportions of the beam will likely not be reflected back to the transducerwhen bouncing off these flaws. Such flaws may be referred to as obliqueflaws.

In view of the foregoing, it would be desirable to provide an ultrasonictransducer arrangement for detecting oblique flaws using pulse-echotesting.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an ultrasonictransducer arrangement for detecting oblique flaws using pulse-echotesting.

This and other objects may be achieved through systems and methods thatutilize an angled ultrasonic transducer that may be mounted on a testingunit and offset from its position if it were to emit a beamperpendicular to the object's outer surface. More specifically, whentesting a cylindrically-shaped object, the transducer may be positionedso that its axis is parallel to a plane that is defined by thelongitudinal axis and a radial axis of the object. When the transduceris actuated, it emits an ultrasonic beam at an angle from the transduceraxis onto the outer surface of the object. The plane defined by theemitted beam and the transducer axis may be parallel to the planedefined by the longitudinal and radial axes of the object.

As a result, this approach may produce shear waves that travel throughthe object along a spiral path that has two components: one componentthat is generally circular and that lies within the plane of theobject's cross section, and one component that is generally along thelength of object. The resulting direction of travel is at a desiredangle, (e.g., a 45-degree angle) from each of the first and secondcomponents.

The magnitude of the offset may depend on the angle between thetransducer axis and the emitted beam (i.e., the setting angle) and maybe proportional to the diameter of the object. The setting angle may bedetermined based on a desired angle at which the emitted beam isdesignated to refract upon entering the object (e.g., a 45-degreerefraction angle), and based on the ratio of the velocity of sound in acoupling medium to the velocity of sound in the object. When detectingflaws in steel tubes while immersing the transducer in water, thesetting angle may be built into the transducer and chosen to beapproximately 13.5 degrees.

The transducer may include a transducer element that is partiallycontained within a cylindrically-shaped housing having one end that isgenerally cut along a plane so as to emit a beam at the desired settingangle. The transducer element may include rods of piezoelectric ceramicmaterial and a polymer material in which the rods are embedded.

One or more transducer of the type(s) described above may be mounted onan ultrasonic inspection system that includes a rotary testing unitconfigured to receive the object to be tested (such as a tube or a bar),and an actuator configured to actuate the transducer(s). Suchtransducers may be used for oblique flaw detection as well as transverseand longitudinal flaw detection, longitudinal wave testing, thicknessmeasurements, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantageswill be more apparent from the following detailed description of thepreferred embodiments, taken in conjunction with the accompanyingdrawings, in which like reference characters refer to like partsthroughout, and in which:

FIG. 1 is a cross-sectional view of a tube with two transducers in aconventional arrangement for performing shear wave testing for detectinglongitudinal flaws;

FIG. 2 is a cross-sectional view of a tube with a single transducer in aconventional arrangement for performing shear wave testing for detectingtransverse flaws;

FIG. 3 is a perspective view of an illustrative transducer in accordancewith certain embodiments of the present invention;

FIG. 4 is a top view of the illustrative transducer of FIG. 3, takengenerally along the line 4-4, in accordance with certain embodiments ofthe present invention;

FIG. 5 is a perspective view of an illustrative rotary tester testing atube in accordance with certain embodiments of the present invention;

FIG. 6 is a cross-sectional view of the rotary tester and tube of FIG.5, taken generally along the line 6-6, and showing the illustrativetransducer of FIGS. 3-4 in accordance with certain embodiments of thepresent invention;

FIG. 7 is a cross-sectional view of the rotary tester and tube of FIG.5, taken generally along the line 7-7, and showing the illustrativetransducer of FIGS. 3-4 in accordance with certain embodiments of thepresent invention; and

FIG. 8 is a perspective view of the tube of FIGS. 5-7 with theillustrative transducer of FIGS. 3-4 and 6-7 positioned for testing inaccordance with certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to systems and methods for inspectingtubes, bars, pipes, and other objects using ultrasonic transducers. Moreparticularly, the invention relates to transducers that are used inpulse-echo testing to detect oblique internal or surface flaws usingshear waves. As discussed above, simply offsetting a transducer withoutangling it, as shown in FIG. 1, can be used to detect longitudinalflaws, while angling a transducer without offsetting it, as shown inFIG. 2, can be used to detect transverse flaws.

In order to detect the more common, naturally occurring, oblique flawsthat are neither transverse nor longitudinal, an approach that combines,yet modifies, both techniques using the same transducer may be providedin the present invention. As a result, this approach may produce shearwaves that travel through the object being tested along a spiral paththat has two components: one component that is generally circular andthat lies within the plane of the object's cross section, and onecomponent that is generally along the length of object. The resultingdirection of travel is at an angle from each of the first and secondcomponents.

FIGS. 3 and 4 offer two views of an illustrative transducer 300 for usein the present invention. FIG. 4, is a view of transducer 300 takengenerally along line 4-4 of FIG. 3. Transducer 300 may be manufacturedso as produce an angled beam that is cylindrically focused.Cylindrically focused transducers provide the desired uniformity interms of detection sensitivity in connection with shear wave testing.

Ultrasonic pulses may be emitted and received from the bottom surface oftransducer 300. Transducer 300 may include transducer element 310 andhousing 330. The bottom part of housing 330 may or may not cover thesurface of transducer element 310, so long as ultrasonic pulses cantravel back and forth from and to transducer element 310. Transducer 300may be cylindrically shaped with a designated angle built intotransducer housing 330. The designated angle (which may also be referredto as the setting angle) may be the angle between the beam emitted bytransducer element 310 and axis 320 which corresponds to the axis ofhousing 330. Housing 330 may be generally cut along a plane that is notperpendicular to axis 320 in order to generate the shape that results inthe beam being angled.

Housing 330 may be roughly 1.75 inches long and may have a diameter ofabout 1 inch. Transducer element 310 may be round and may have adiameter of about 0.6 inches. Such transducers are appropriate fortesting bars and tubes with an outer diameter of approximately 2.5inches. Best results may be achieved when the beams emitted by thesetransducers are focused at a point along the longitudinal axis of thetested tube or bar. Accordingly, the focal length of transducer element310 may be 2.5 inches. Although several beams may emanate fromtransducer element 310, a single beam may be referred to as beingemitted along a path that connects the center of element 310 with thepoint into which the constituent beams are focused.

It is understood that while transducer 300 is illustrated as asingle-element transducer, a multi-element transducer arranged in alinear array or along multiple rows may alternatively be provided. It isalso understood that the present invention may be used with bars andtubes of any suitable outer diameters.

Transducer element 310 may be made of any suitable material such aspiezoelectric material. Transducer element 310 is preferably made ofthin rods of piezoelectric ceramic elements embedded into a polymermaterial. The electrical and ultrasonic properties of transducer 300 maydepend on the microstructure and the properties of the materialsconstituting transducer element 310. Transducer 300 may be connected toa coaxial cable (not shown) such that electric signals sent through thecable may drive transducer element 310. Similarly, echoes received bytransducer element may be communicated through electric signals throughthe cable.

The previous discussion relating to FIGS. 3 and 4 describes oneparticular embodiment of transducer 300. However, the dimensions andproperties of transducer 300 are not limited to the ones mentioned aboveand may be varied based on the dimensions and properties of the objectto be tested or other considerations.

FIG. 5 illustrates a tube 530 being tested by rotary tester 500. Tube530 has longitudinal axis 550. The main body of tester 500 may beenclosed within a cubical frame 505, from which two outer shafts 510 mayextend. Tube 530 may enter tester 500 from one of outer shafts 510 suchthat the center of tube 530 (i.e., longitudinal axis 550) passes throughthe centers of shafts 510 and tester 500. Tube 530 may also be allowedto move freely in direction 560 along the tube's longitudinal axis 550without directly coming in contact with any part of tester 500. Tube 530is shown to have inner surface 532 and outer surface 534. Tester 500 mayinclude a testing unit (not shown in FIG. 5, but shown in FIGS. 6 and7), which is enclosed within cubical frame 505. Hoses 520 and 521 can beused to deliver and cycle coupling medium to and through tester 500. Thecoupling medium (not shown in FIG. 5, but shown in FIGS. 6 and 7) may beany suitable medium in which ultrasonic waves may propagate freely.Water may be chosen as coupling medium mainly because it is inexpensive.As tube 530 is being tested, the coupling medium may be deliveredthrough hose 520 at one of outer shafts 510, while the coupling mediummay exit through hose 521 at the other outer shaft 510. As tube 530 ismoved through tester 500, the coupling medium may be pumped and cycledthrough the testing unit in tester 500. Shafts 510 may include sealsthat may keep the water contained within the testing unit.

As previously mentioned, tube 530 may be rotated about axis 550 as it isbeing tested. However, as shown in FIG. 6, which is a cross-sectionalview of rotary tester 500 and tube 530 taken generally along line 6-6 ofFIG. 5, testing unit 540, which is enclosed within cubical frame 505,may be rotated about axis 550 in, for example, counter-clockwisedirection 565. Coupling medium 525 remains in contact with both theouter surface 534 of tube 530 and the inner wall 542 of testing unit540, therefore filling the space between tube 530 and testing unit 540during testing. The rotational speed may be between 1800 and 4000 RPM,allowing a testing speed of up to 400 feet per minute.

In addition to longitudinal axis 550, which intersects the centers ofboth tube 530 and testing unit 540, there is radial axis 555, which isperpendicular to and intersects longitudinal axis 550, and which lieswithin the plane of FIG. 6. Transducer 300 may be mounted within testingunit 540 so as to test for oblique flaws. As such, transducer 300, whichis angled, may be mounted within testing unit 540 and offset indirection 580 from its position if it were to emit a beam perpendicularto tube 530's outer surface 534, as shown in FIG. 6. As a result, theemitted ultrasonic beam 570 is not perpendicular to tube 530's outersurface 534.

Because the angle of incidence is not 90 degrees, a portion of theincident beam 270 may be refracted at the interface between couplingmedium 525 and outer surface 534 of tube 530. As illustrated, refractedbeam 575 may bounce between inner surface 532 and outer surface 534 oftube 530, traveling in a direction that has two components: onecomponent that is generally circular and that lies within the planeshown in FIG. 6 (i.e., the plane of tube 530's cross section), and onecomponent that is generally along the length of tube 530 (i.e., withinthe plane containing radial axis 555 and longitudinal axis 550) as shownin FIG. 7. As a result, beam 575 may travel along a spiral path throughtube 530, partly reflecting between inner surface 532 and outer surface534, until beam 575 reaches a flaw 590 (which may be an oblique flaw).Beam 575 may then be reflected back from flaw 590 and refracted beforereaching transducer 300 as beam 570.

The offset in direction 580 may be in either direction away from radialaxis 555, provided the offset is contained within the same plane that isperpendicular to longitudinal axis 550 and that contains radial axis555. These conditions hold as testing unit 540 and transducer 300 arerotated about longitudinal axis 550. The amount of the offset indirection 580 may depend on various factors such as the material beingtested (the velocity of sound in the material of tube 530), the diameterof tube 530, etc.

As illustrated in FIG. 6, one component of the direction in whichrefracted beam 575 may travel may be a generally clockwise componentthat lies within the plane containing the cross section shown for tube530. This component may be achieved by offsetting transducer 300 fromaxis 555 along direction 580. The magnitude of offset may beproportional to the diameter of tube 530 and may be reset for everydiameter. As such, transducer 300 may be mounted on a rotatable disk(not shown) which may be affixed to testing unit 540 and adjusted toobtain the desired offset. To produce a refracted shear beam thattravels in a direction having a counter-clockwise component, transducer300 may simply be offset from axis 555, in the direction opposite todirection 580.

The other component of the direction in which refracted beam 575 maytravel may be generally along the length of the tube and may be withinthe plane containing the tube's radial and longitudinal axes 555 and550. The fact that the transducer is angled achieves this component.FIG. 7, which is a cross-sectional view of rotary tester 500 and tube530 taken generally along line 7-7 of FIG. 5, shows testing transducer300 emitting beam 570 in addition to being offset as shown in FIG. 6.Beam 570 is angled in a plane that is parallel to longitudinal axis 550.As discussed above, refracted beam 575 may travel through tube 530,partly reflecting between inner surface 532 and outer surface 534, untilbeam 575 reaches oblique flaw 590 and is reflected back and refractedbefore reaching transducer 300 as beam 570.

The component of the direction along which beam 575 is shown to betraveling in FIG. 7 is generally along direction 560. This may bereferred to as forward-looking shear wave testing. Alternatively,transducer 300 may be rotated 180 degrees about radial axis 555 toproduce beams that travel in the opposite direction for reverse-lookingshear wave testing.

The foregoing describes a technique that can be used to detect obliqueflaw 590 using a single transducer 300 that produces refracted beam 575that may travel through tube 530 along a spiral path that has twocomponents: one that is generally circular and that lies within theplane of tube 530's cross section, and one that is generally along thelength of tube 530. The resulting direction from summing these twocomponents may be at a desired angle from each of the components. Forexample, the desired angle may be a 45-degree angle or any otherangle(s).

FIG. 8 is a perspective view of tube 530 of FIGS. 5-7 with transducer300 of FIGS. 3-7 positioned for testing for oblique flaws according tothe above discussion. Transducer 300 may be shaped so as to produceangled beam 570. Transducer 300 may also be offset in direction 580.However, the challenge lies in designating the appropriate incidentangle that may be built into transducer 300 (which may be referred to assetting angle 802) and the amount by which transducer 300 may be offset(which may be referred to as offset 804) so as to effectively detectoblique flaws. The discussion below describes how setting angle 802 andoffset 804 may be calculated.

In the configuration shown in FIG. 8, transducer 300 may be positionedso as to emit beam 570 which may enter tube 530 at point of generalincidence 808. Radial axis 855 of tube 230 may be the radial axis alongwhich a non-angled transducer would be positioned if it were to emit abeam perpendicular to outer surface 534 of tube 530 for longitudinalwave testing. Radial axis 855 and longitudinal axis 550 may be containedwithin plane 818. Transducer axis 320 and incident beam 570 may becontained in plane 812. Point of general incidence 808 may also belocated on plane 812. Planes 812 and 818 may be parallel and thedistance between them may correspond to offset 804. Setting angle 802may correspond to the angle between incident beam 570 and transduceraxis 320.

Radial axis 856 of tube 230, on the other hand, may be the radial axiswhich intersects outer surface 534 of tube 230 at point of generalincidence 808. The angle of incidence (i.e., incident angle 810) maycorrespond to the angle between incident beam 570 and radial axis 856.The relationship between incident angle 810 and setting angle 802 may begeometrically calculated as follows:

${{SettinAngle}\; 802} = {\arcsin( {\sqrt{2}{\sin( \frac{{IncidentAngle}\; 810}{2} )}} )}$

Offset 804 may be proportional to the diameter of the tested object andmay depend on the setting angle. More particularly, offset 804, whichdepends on external diameter 816 of tube 230 may be calculated asfollows:

${{Offset}\; 8804} = {\frac{{Diameter}\; 816}{2}{\sin( {{SettingAngle}\; 802} )}}$

The above equations may be used to determine the setting angle for atransducer and the amount at which it may be offset based on a desiredincident angle that may be best suited for testing for oblique flaws.The incident angle may be determined in accordance with Snell's law,which states that the ratio of the sine of the incident angle to thesine of the angle of refraction angle equals the ratio of the soundvelocity in the medium of incidence to the sound velocity in the mediumof refraction.

The ratio of the sound velocity in the medium of incidence to the soundvelocity in the medium of refraction may be referred to as υ and thedesired refraction angle may be referred to as α_(r). Accordingly, theequation set forth above for calculating the setting angle (which may bereferred to as α_(s)) may be rewritten as follows:

$\alpha_{s} = {\arcsin( {\sqrt{2}{\sin( \frac{\arcsin( {\upsilon\;\sin\;\alpha_{r}} )}{2} )}} )}$

When steel tubes are tested (i.e., the medium of refraction is steel)and water is used as coupling medium (i.e., the medium of incidence iswater), the water-to-steel velocity ratio υ is approximately 0.4748. Therefraction angle α_(r) is generally chosen to be 45 degrees so thatsubstantial portions of the beam may be reflected back towards thetransducer along the same path to ensure detectability. Plugging suchvalues into the last equation set forth above yields a designatedsetting angle of approximately 13.5 degrees for detecting oblique flawsin steel tubes using an offset transducer immersed in water. Therefraction angle α_(r) may vary within +/−5 degrees to maintain reliabledetectability. Alternatively, any other refraction angle in reference tothe cross section of the tube may be chosen. Similarly, the settingangle α_(s) may vary by +/−2 degrees and may be different from the angleused for transverse flaw detection in which the transducer is nothorizontally offset.

Thus, once the coupling medium and tested material are chosen, choosingan appropriate setting angle that may be built into the transducer (orat which a-regular transducer—i.e., one that does not have an emissionangle built in—may be tilted) to detect oblique flaws may merely dependon the desired refraction angle in the object to be tested.

Referring to the external diameter of the tested object as D, theequation set forth above for calculating the offset, which may also bereferred to as A, may be rewritten as follows:

$A = {\frac{D}{2}{\sin( \alpha_{s} )}}$

Referring back to FIGS. 5-8, transducer 300 may be mounted so as toperform shear wave testing. While tube 530 is moved in direction 560,the transducer may rotate about longitudinal axis 550 in direction 565during testing. This combination of motions results in helical testtraces around the circumference of tube 530. These traces slightlyoverlap to ensure reliable flaw detection and achieve 100 percentinspection. Additional transducers may also be used for longitudinalwave testing, thickness measurements, transverse flaw detection,longitudinal flaw detection, etc.

Several transducers 300 may be used in rotary tester 500 to detect thelargest range of orientation of angles possible for oblique flaws inaddition to a basic setup that utilizes five transducers for performingclockwise and counter-clockwise longitudinal, forward and reversetransverse flaw detection and a wall thickness measurement. For example,a first transducer 300, may be used for performing clockwise,forward-looking shear wave testing. A second may be used for performingcounter-clockwise, forward-looking shear wave testing. A third may beused for performing clockwise, reverse-looking shear wave testing. Afourth may be used for performing counter-clockwise, reverse-lookingshear wave testing. Moreover, in case it is required to cover the rangeof 25-to-45 degrees of directions, an additional transducer may beassigned to each five degrees of increments.

Several problems may be nevertheless associated with increasing thenumber of transducers used. Because each transducer may require aseparate channel, the number of channels used for analyzing the signalsemitted and received from transducers would increase. Accordingly, thenumber of required coupling capacitors would also increase. In turn,this would complicate the required rotary connections. However, rotarytesters have a limited number of testing channels available and largenumber of channels require longer changeover time from one size of tubeto another. Although the signals received from individual transducersmay be multiplexed to decrease the number of channels, the inspectionspeed may significantly diminish in order to preserve reliability.Furthermore, the mounting space on the rotor may be limited andtransducer cross-talk can become a greater problem.

Fortunately, cracks in pipes and tubes are more likely to occur inspecific directions depending on the manufacturing process. Thesedirections and corresponding angles can be identified during production.For example, if a diagonal rolling motion is encountered, theorientation of defects may be determined by the rolling direction.Manufacturers may therefore specify direction and angle requirements fordetecting oblique flaws, and a reduced number of transducers may be usedto fit such requirements. For example, with respect to a requirement foroblique detection capability adjustable to 35+/−10 degrees in twodirections, two transducers 300 may be used so long as one performsclockwise shear wave testing, and the other, counter-clockwise shearwave testing. In such a case, the number of testing transducers, hencethe number of channels, required for reliable longitudinal, transverseand oblique flaw detection can be limited to six, with only two of thembeing transducers that are dedicated to detect oblique flaws oriented indifferent directions, such as transducer 300.

Therefore, reliable oblique flaw detection may be achieved withoutreducing inspection speed, significantly adding to transducercross-talk, or requiring significant electronic hardware or processingadditions such as multiple transducers, coupling capacitors, connectionsand testing channels. Moreover, no additional mounting hardware would berequired because the transducers that are designed for oblique flawdetection may have the designated angle built into their housing asshown in FIGS. 3 and 4. Alternatively, a regular transducer may also beused to detect oblique flaws if additional hardware is available to tiltthe transducer so as to emit the desired angled beam. For higherinspection speeds or thickness measurements, additional hardware andprocessing may be required.

Thus it is seen that systems and methods for horizontally offsetting asmall number of angled transducers that each use pulse-echo testing togenerate shear waves for detecting oblique surface and internal flawshave been provided.

One of ordinary skill in the art should appreciate that the presentinvention may be practiced in embodiments other than those describedherein. For example, angled and offset transducers may be used in atesting apparatus other than a rotary tester. Moreover, the transducersdescribed above may be used to test a flat object, such as a plate,without moving about its surface.

It will be understood that the foregoing is only illustrative of theprinciples of the present invention, and that various modifications canbe made by those skilled in the art without departing from the scope andspirit of the invention, and the invention is limited only by the claimsthat follow.

What is claimed is:
 1. A method, comprising: causing a transducer toemit a beam that is focused at a point and emitted toward a surface ofan object, wherein the emitted beam contacts the surface at obliqueangles, such that a refracted beam travels through a portion of theobject along multiple directions when the transducer emits the beam. 2.The method of claim 1, wherein the beam is a cylindrically focused beamhaving a focal length substantially equal to a diameter of the object.3. The method of claim 1, wherein a position of the transducer is at anoffset and an angle relative to the object, and the position causes theemitted beam to contact the surface at the oblique angles.
 4. The methodof claim 3, wherein the offset is based at least in part on the angle.5. The method of claim 3, wherein the offset is based at least in parton a diameter of the object.
 6. The method of claim 3, wherein theoffset is in a direction perpendicular to a radial axis of the object.7. The method of claim 3, wherein the angle is in a first plane parallelto a second plane defined by the longitudinal axis of the object and aradial axis of the object.
 8. The method of claim 3, wherein themultiple directions include a first direction that is substantiallycyclical and lies within a plane of a cross section of the object and asecond direction that is substantially parallel to the longitudinal axisof the object.
 9. The method of claim 1, further comprising determiningwhether a flaw exists in the object.
 10. The method of claim 9, furthercomprising receiving a reflected signal caused by a partial reflectionof the refracted beam in the object, wherein determining whether a flawexists in the object comprises comparing the emitted beam with thereflected signal.
 11. A system, comprising: a transducer configured toemit a beam toward a surface of an object, wherein: the beam is focusedat a point, and the emitted beam contacts the surface at oblique angles,such that a refracted beam travels through a portion of the object alongmultiple directions when the transducer emits the beam.
 12. The systemof claim 11, wherein the beam is a cylindrically focused beam having afocal length substantially equal to a diameter of the object.
 13. Thesystem of claim 11, wherein a position of the transducer is at an offsetand an angle relative to the object, and the position causes the emittedbeam to contact the surface at the oblique angles.
 14. The system ofclaim 13, wherein the offset is based at least in part on the angle. 15.The system of claim 13, wherein the offset is based at least in part ona diameter of the object.
 16. The system of claim 13, wherein the offsetis in a direction perpendicular to a radial axis of the object.
 17. Thesystem of claim 13, wherein the angle is in a first plane parallel to asecond plane defined by the longitudinal axis of the object and a radialaxis of the object.
 18. The system of claim 13, wherein the multipledirections include a first direction that is substantially cyclical andlies within a plane of a cross section of the object and a seconddirection that is substantially parallel to the longitudinal axis of theobject.
 19. The system of claim 11 further comprising a flaw detectorconfigured to determine whether a flaw exists in the object.
 20. Thesystem of claim 19, wherein the flaw detector determines whether a flawexists in the object by comparing the emitted beam with a reflectedsignal caused by a partial reflection of the refracted beam in theobject.